For example, in a transmitter for a mobile communication system which adopts the code division multiple access communication (CDMA: Code Division Multiple Access) mode and the like for radio communications, a signal to be a transmission target (transmitting signal) is processed by a digital modulating part.
FIG. 6 shows an exemplary configuration of a transmitting amplifier.
In a digital modulating part 51 in this example, signals on a plurality of n of carriers are inputted to a baseband limiter (BB limiter) 61, the signals on the carriers outputted from the BB limiter 61 pass through band limiting filters F1 to Fn, up filters (Up filters) G1 to Gn and digital quadrature modulating parts H1 to Hn, they are added by an adder 62, and the added result is outputted.
In the subsequent stage of the digital modulating part 51, a D/A (Digital to Analog) converter 71, a frequency converting part 72, and a power amplifier (PA: Power Amplifier) 73 are provided. The output signal from the adder 62 passes therethrough for output. In this manner, the peak factor of the transmitting signal is made small, whereby the range of the amplifiable level of the power amplifier is compressed to intend power saving as well as the reproduction of the inverse characteristic of distortion is made easier in distortion compensation of a pre-distortion mode.
In addition, such a transmitter is known in which for an intermediate frequency signal after each carrier synthesis (that is, the output signal of the adder 12), a window function is multiplied around a peak to suppress the peak (for example, see Patent Reference 2).
Patent Reference 1: JP-A-2004-166245
Patent Reference 2: JP-A-2005-20505